I have'nt done much with Automator myself, but I do believe you can run Applescripts in Automator workflows, and there is a Unix command line utility called "md5" that returns a checksum on any files or folders supplied to it, if you open up the Terminal app and type this into the command line followed by the return key.
this will return the checksum for the file if it is a valid file path, for more info on the md5 command, type this into the terminal.
this will return the manual for the md5 utility, I dont know if the same utility can be used for drive paths as well, or if there is another command line tool for your purposes, you may have to check that with one of the Unix tools websites.
If you do know any Applescript coding, then you can design a Applescript droplet that runs a shell script command to the md5 utility, when a file or folder or drive is dropped onto your droplet application, for example.
Code:
on run
set filePath to POSIX path of (path to documents folder) & "MyTextFile.txt" as text
set theResult to do shell script "md5" & space & quoted form of filePath
return theResult
end run
This will return the checksum result on a file called MyTextFile.txt in your Documents folder.
If you put this code into a on open handler instead of an on run handler, then it will return the same result when files are dropped onto your compiled droplet application.
Like Automator, I dont know a lot of Applescript, but I always go to the MacScripter forums for help with my scripts, there are some really smart and knowledgable guys over there, that could probably come up a a trick Applescript solution for you.
MacScripter
Sorry I could not be more help.
Regards Mark